Abstract The HuR (elavl1) family of RNA binding proteins (RBPs) posttranscriptionally regulates the expression of a number of pro-inflammatory genes involved in immunity, autoimmunity, and allergy. HuR binds to AU-rich elements (AREs) in 3' untranslated regions (UTRs) of labile mRNA transcripts to stabilize and recruit them to heavy polysomes. However, the mechanisms by which posttranscriptional gene regulation controls CD4+ T cell differentiation and activation are unclear, despite the fact that many pro-inflammatory factors such as cytokines and chemokines are regulated at this level by RBPs. Genome wide array analysis has identified multiple asthma related genes. However, such broad approaches may overlook relevant genes, as there is a poor correlation between steady-state mRNA levels and protein. In order to overcome these limitations, methods such as RNA immunoprecipitation applied either to microarrays or deep sequencing (RIP-Chip or RIP-Seq) have been developed. RIP-Seq identifies genes for which steady-state mRNA levels do not significantly change. The work herein proposed supports the long term goal of understanding posttranscriptional gene regulation in CD4+ T cell- mediated inflammation. The objective of this application, is to understand how HuR regulates key molecules involved in the activation and proliferation of CD4+ T cells during responses to antigen. The central hypothesis is that HuR is required for antigen-specific activation and proliferation of CD4+ T cells. The rationale for this proposal stems from reports demonstrating that HuR regulates Th2 cytokine production through stabilization of relevant mRNAs and is also important for Th2 differentiation. Preliminary results suggest that HuR plays a critical role in IL-2 homeostasis. IL-2 is one of the first cytokines made by T cells soon after activation. CD4+ T cells from OVA-immunized HuR KO mice also showed severe defects in antigen-specific proliferative responses. In an allergic airway inflammatory model, OVA-challenged HuR KO mice had decreased lung cellular infiltration. Understanding posttranscriptional mechanisms which govern T cell activation will allow the field to develop therapies to direct outcomes of inflammatory responses in multiple autoimmune diseases. Additionally, such knowledge can have broad implications to T cell biology in general. The central hypothesis will be tested and the proposal's objectives accomplished by the following two specific aims: 1) Determine the effect of HuR deletion on antigen-specific CD4+ T cell activation, 2) Define the mechanisms by which HuR deletion alters T cell function. The proposed study is innovative because using both RNA-Seq and RIP-Seq in concert will allow for identification of novel networks of HuR targets that are critical to normal antigen-specific responses. The research is significant because it will improve the field's understanding of posttranscriptional modulation of antigen-specific T cell activation and proliferation, as well as identifying HuR targets vital to allergic airway inflammation.